Wireless networks are prevalently used in the public safety sector (e.g., police, fire fighters, emergency workers, etc.). Such networks include, for example, Association of Public Safety Communications Officials (APCO) Project 25 (P25) compliant wireless networks, and those specified by the European Telecommunications Standards Institute (ETSI)'s digital wireless communication device (DMR) Tier-2 Standard.
P25 standards are produced through the joint efforts of the Association of Public Safety Communications Officials International (APCO), the National Association of State Telecommunications Directors (NASTD), selected Federal Agencies and the National Communications System (NCS), and standardized in specifications issued by the Telecommunications Industry Association (TIA), standard committee TR-8. Further details regarding the P25 standards can be obtained from the Telecommunications Industry Association, 2500 Wilson Boulevard, Suite 300 Arlington, Va. 22201. P25 specifies to a suite of narrowband digital Land Mobile Radio (LMR) communication standards for digital radio communications, equipment and systems. The P25 TIA series of documents (TIA-102) describe an open architecture for Public Safety mission critical digital radio communications. The goal of Project 25 (P25) is to provide an open standard that enables multiagency or regional LMR interoperability.
The ETSI DMR Tier-2 Standards have been and are currently being developed by ETSI, and any of the DMR standards or specifications referred to herein may be obtained by contacting ETSI at ETSI Secretariat, 650, route des Lucioles, 06921 Sophia-Antipolis Cedex, FRANCE.
The APCO P25 standards for digital two-way radio technology and the ETSI DMR Tier-2 standards are incorporated by reference herein in their entirety.
Within a P25 network or system there are a number of standardized interfaces. For example, the P25 standards specify a Common Air Interface (CAI) and related trunking standards provide for interoperability on a subscriber unit level. Among other things, the CAI defines the type and content of signals transmitted by P25-compliant radios. For instance, Project 25 Phase I compliant communication systems implement an FDMA-based channel access scheme, whereas Project 25 Phase II compliant communication systems implement a TDMA-based channel access scheme.
The public safety sector has recognized the need of connecting different Radio Frequency Sub-System (RFSS) together to form a larger network with a much larger coverage. Based on this need, the TIA TR8 committee has also developed the Intra-Radio Frequency (RF) Sub-Systems Interface (ISSI). The ISSI is defined in TIA-102.BACA-A, January 2009, and several addendums and other documents. TIA-102.BACA-A, January 2009 specifies the ISSI Messages and Procedures for Voice and Mobility Management Services. The ISSI is a non-proprietary multi-channel digital interface that specifies protocols having the capabilities needed to interconnect two or more core P25 radio networks (e.g., built by different manufacturers) together into one or more wide-area networks (WANs). The core P25 radio networks are called Radio Frequency Sub-Systems (RFSSs). The ISSI gives system designers the flexibility to combine any number of radio frequency sub-systems of any size. For example, the ISSI will allow network administrators to connect to other local, regional, statewide or federal networks. The ISSI supports standard Internet Protocol (IP)-based protocols for the transport of information to enable interoperability for different radio frequency sub-systems and to provide a common meeting place for radio frequency sub-systems of different technologies (Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA), micro-cell) and different RF bands. For example, the call signaling protocol is based on Session Invitation Protocol (SIP), which is specified in the Internet Engineering Task Force (IETF) Request For Comments (RFC) 3261, while the voice traffic and push-to-talk control messages are carried through the use of Real Time Protocol (RTP), which is specified in RFC 3550.
The wide area network connections using the ISSI provide an extended coverage area for subscriber units (SUs) that are roaming. For example, the ISSI performs mobility management functions and procedures to allow roaming (mobility) of subscriber units between radio frequency sub-systems. For instance, the ISSI supports the messaging and procedures necessary to enable radio frequency sub-systems to track and locate subscriber units, set-up and teardown calls and transfer voice information to the subscriber units. The ISSI uses standardized protocols (e.g., SIP and RTP protocols) to provide the messaging between radio frequency sub-systems. This allows subscriber units from a home radio frequency sub-system (HRFSS) to operate at another serving radio frequency sub-system (SRFSS) as if the subscriber units were operating in their HRFSS. The extended coverage area is important, for instance, to public safety first responders that provide assistance in other jurisdictions during an emergency.
In P25 systems, each radio frequency sub-system maintains a registration database. The registration database includes subscriber unit registration information that identifies which radio frequency sub-system(s) particular subscriber unit identifiers (SUIDs) are currently authorized to be registered with, the home radio frequency sub-system for each subscriber unit ID, and talk group (TG) registration information that identifies a HRFSS for each talk group, and other radio frequency sub-system(s) that talk groups (TGs) that are currently authorized to be registered with. A talk group is registered with a radio frequency sub-system if one or more subscriber units that are registered with that radio frequency sub-system belong to the talk group, and the HRFSS of that talk group has authorized registration of the talk group at that radio frequency sub-system. A SRFSS registers subscriber units/talk groups with a HRFSS so that subscriber units that are registered with the SRFSS can continue to receive calls from the HRFSS after the subscriber units roam to the SRFSS. For example, a SRFSS would register a subscriber unit/talk group with its HRFSS so that the HRFSS knows that it should forward any calls that originate in the HRFSS and are intended for that subscriber unit (or for a talk group that the subscriber unit belongs to) to the SRFSS so that the “roamed” subscriber unit will continue to receive calls.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments.
The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments described herein so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.